This invention relates to image transmission systems, such as advanced television systems.
Scanning format is a consideration in the design of image transmission systems. Two formats typically considered are progressive and interlaced scanning. Each format breaks up an image into an array of lines. In a progressive scanning system, each of a succession of image frames contains all of the lines representing an image. In an interlaced scanning system, there are a succession of fields, each containing half of the lines of an image; every other field contains the odd lines of the image, and the other fields contain the even lines. Interlacing can reduce the data rate of the television camera or receiver, as only half of the pixels forming an image are processed for each field.
Both interlaced and progressive scanning have been proposed for advanced television systems (e.g., for the United States HDTV standard). Progressive scanning produces better image quality; artifacts (e.g., flicker) resulting from interlaced scanning are avoided, and smoother motion rendition is achieved (important, e.g., for sporting events). Progressive scanning also has the advantage of being easier to interface with computers and telecommunication networks. But interlaced scanning has the advantage of being compatible with existing production and display technology, and thus would, at least in the short run, reduce the cost of implementing an advanced television system. For the same bandwidth, interlaced scanning is also capable of producing a greater number of lines than progressive scanning, and this is viewed by some of its proponents as producing improved spatial resolution and image sharpness.
Television source material has certain non-program-content characteristics, such as frame rate, spatial resolution, and scanning format (such as interlaced or progressive). Conventional television transmission systems convert the source material to a common format prior to transmission, so that these non-program-content characteristics are not retained. For example, 24 frame-per-second film is converted to 60 fields-per-second video using the 3:2 pull-down method, and low spatial resolution material is converted to the same resolution as high resolution material.
My U.S. Pat. No. 5,187,575 (hereby incorporated by reference) teaches that some non-program-content characteristics (e.g., frame rate, spatial resolution, scanning format) can be retained in the transmitted signal with resulting improvement in image quality.